1. Field of the Invention
This invention generally relates to a one-way clutch, and, in particular, to an sprag outer retainer ring of a sprag-synchronized one-way clutch assembly.
2. Description of the Prior Art
A sprag-synchronized one-way clutch is well known in the art and one such example is schematically shown in FIG. 1. As shown, a sprag-synchronized one-way clutch assembly 1 is typically interposed between an inner ring 2 and an outer ring 3, which are provided to be rotatable concentrically and relative to each other. When the inner and outer rings 2 and 3 try to rotate in the opposite directions indicated by the arrows in FIG. 1, the relative rotation between the inner and outer rings 2 and 3 are prevented by the one-way clutch assembly 1; whereas, if the inner and outer rings 2 and 3 are driven to rotate in the opposite directions and opposite to the directions indicated by the arrows, a relative rotation between the inner and outer rings 2 and 3 is allowed to take place.
The sprag-synchronized one-way clutch assembly 1 includes a pair of outer and inner retainer rings 4 and 5, each of which is formed with a plurality of sprag insertion holes 4a and 5a, respectively, as arranged in the circumferential direction as spaced apart from one another at a predetermined pitch. The assembly 1 includes a plurality of sprags 6 arranged in the circumferential direction, each of which has a particular cross-sectional shape similar to the figure of "8." Each of the plurality of sprags 6 is set in position with its upper portion fitted into a corresponding sprag insertion hole 4a formed in the sprag outer retainer ring 4 and its lower portion fitted into a corresponding sprag insertion hole 5a formed in the sprag inner retainer ring 5. Preferably, each of the sprags 6 has an outer cam surface 6a and an inner cam surface 6b, each of which is defined by one, two or more radii of curvature.
Also provided between the sprag inner and outer retainers 4 and 5 of the assembly 1 is a ribbon spring 7 which is used to normally impart a moment to each of the sprags 6 in a predetermined direction. The ribbon spring 7 is formed with a plurality of sprag insertion holes 7a as spaced apart from one another at a predetermined pitch, and when the sprags 6 are set in position, the central portion of each of the sprags 6 is supported by the ribbon spring 7. The ribbon spring 7 is generally elongated in shape and made of a relatively thin plate. When the ribbon spring 7 is set in position with each of the sprags 6 inserted in the corresponding sprag insertion hole 7a, the opposite ends of the ribbon spring 7 are brought together to form a generally ring shape. The ring-shaped ribbon spring 7 is located between the outer and inner retainer rings 4 and 5. As shown in FIG. 1, when assembled, the ribbon spring 7 always applies a moment to each of the sprags 6 in the direction indicated by arrows A, so that all of the sprags 6 are given a tendency to be brought into contact with the inner and outer rings 2 and 3.
The general structure of the ribbon spring 7 is illustrated in FIGS. 2a and 2b. In the illustrated example, the ribbon spring 7 is elongated in shape and comprised of a thin plate of stainless steel or the like, and a plurality of generally C-shaped sprag insertion holes 7a are formed at a predetermined pitch. A tab 7d having a predetermined width is formed in each of the sprag insertion holes 7a as a projection projecting into the corresponding hole 7a in a predetermined direction from one side edge of the hole. FIG. 2b is a side view of the ribbon spring 7 shown in FIG. 2a. The illustrated ribbon spring 7 includes a pair of side sections 7b, 7b and a plurality of cross-bar or bridge sections 7c, each extending between the pair of side sections 7b, 7b, arranged in a longitudinal direction as spaced apart from one another at a predetermined pitch. And, a sprag insertion hole 7a is defined by the pair of side sections 7b, 7b and a pair of bridge sections 7c, 7c. In addition, the tab 7d is formed as projecting into the sprag insertion hole 7a from one side edge of the corresponding bridge section 7c. As a result, the sprag insertion hole 7a is constructed generally in the shape of letter "C."
The ribbon spring 7 is provided for imparting a moment to each of the sprags 6 in a predetermined direction indicated by arrows A shown in FIG. 1 so as to provide a tendency for the sprags 6 to be brought into contact with the inner and outer rings 2 and 3 to thereby establish a clutched condition. For this purpose, the tab 7d is required to apply an appropriate pressing force to the associated sprag 6. Furthermore, a wavy bent portion or wrinkle 7e is formed in the ribbon spring 7 at a predetermined pitch along the longitudinal axis of the ribbon spring 7. In the illustrated example, the wrinkles 7e are provided at the same pitch as that of the sprag insertion holes 7a. The wrinkles 7e are formed as bent in a predetermined shape at the same side of the spring 7, and each of the wrinkles 7e is formed as extending across the pair of side sections 7b, 7b and the corresponding tab 7d.
FIG. 3 illustrates the condition in which sprags 6 are set in position as inserted in the corresponding insertion holes 4a of the outer retainer ring 4. Each of the sprag insertion holes 4a is generally in the shape of a rectangle and a notch 4b is formed at the right side edge of each of the sprag insertion holes 4a. The notch 4b is formed by cutting away or removing a part of the side portion of the sprag insertion hole 4a which corresponds in position to the tab 7d so as to avoid any interference in motion with the tab 7d of the ribbon spring 7. That is, the tab 7d moves up and down in accordance with the operation of the one-way clutch assembly 1, and, in order to prevent the tab 7d from being interfered in this up and down motion, the notch 4b is formed to provide a relief space for the tab 7d. As shown in FIG. 2a, tab 7d is provided only at one side edge of the bridge section 7c, and, since the tab 7d is supposed to serve as an element for pushing the associated sprag 6 in its locked or clutched position, it is formed as projecting in the lock direction. Thus, in the case of one-way clutch assembly having an opposite lock direction, it is necessary to provide the notch 4b at the opposite side edge of the insertion hole as shown in FIG. 4. In this manner, since the lock direction can be either one of the two, it is necessary to prepare two kinds of outer retainers 4 different in the location of the notch 4b. The outer retainer 4 is also formed with a flange 4c which is typically formed with a so-called T-bar as a means for securely attaching the outer retainer 4 to the outer ring 3.
The structure of the sprag insertion hole 4a formed in the prior art outer retainer 4 is illustrated in FIG. 5. As shown, the notch 4b generally rectangular in shape is formed at one side edge of the generally rectangularly shaped sprag insertion hole 4a. FIG. 6 is a perspective view showing the above-described prior art outer retainer ring 4 formed with notches 4b, each formed at one side edge of each of the sprag insertion holes 4a. Such a sprag insertion hole 4a which has a notch 4b at one side edge is normally formed by stamping, and one such example of stamping process is shown in FIG. 7. As shown, a ring-shaped outer retainer 4 is placed on a die 10 and a punch 11 having a predetermined cross-sectional shape is pushed into a hole of the die 10 as indicated by the white arrow, so that a sprag insertion hole 4a having a notch 4b can be formed at the same time. Such a sprag insertion hole 4a having a notch 4b is often termed as a pocket in its entirety, and a high dimensional precision is required for such a pocket because of the necessity to synchronize all of the sprags 6 inserted in the respective pockets. However, in the pocket of the prior art outer retainer 4, since the notch 4b is provided only at one side edge of the sprag insertion hole 4a, the pocket as a whole is asymmetrical in shape. Because of this, management of clearance between the die 10 and the punch 11 in press operation is extremely difficult, and skills and exorbitant amount of time were required for this press operation so as to maintain the required high precision. This problem mainly stems from the fact that a clearance D1 at the side edge of the sprag insertion hole 4a where no notch is provided differs, in general, from a clearance D2 at the other side edge where the notch 4b is provided.